That sounds bizarre to me if the grey can be covered with a dark colour it can definetly can be covered wih a lighter colour and also the grey will show so much less as the hair grows. I am going to suggest you either try another hairdresser or and I wouldnít normal encourage home colouring but just to prove a point and help you I am going to in your case. ...More >
Ask for help in a store to match the colour of your ends in order to choose a root colour, I suggest a level 6 or 7 so something called lightest brown or dark blonde. Please buy 2 boxes one of the 6 or 7 that say N or .0 and one that says its .1 or ash.
Mix half each of the natural colour and the ash colour approx 60mls of colour then mix only 40mls of the developer (20 vol / 3%) then apply liberally to your roots making sure your hair is clean and dry. Process for 40 / 45 mins regardless of the instructions. After 30 mins mix the remainder of the chosen base colour .0 or N with equal parts of water & developer - apply to the mid lengths and ends of your hair and process. Rinse and shampoo the colour from your hair and I am sure you will have a super result.